Methods to isolate and to serially cultivate rabbit and human skin epidermal keratinocytes are being developed. The major factors that affect the growth of keratinocytes in vitro are being investigated. Using populations of replicative and non-replicative cells, the changes in the constituent proteins in each cell population that take place during the interconversion are being investigated by gel electrophoresis. The growth characteristics of the sebocyte from human and rabbit skin are being defined, and the effect of hormones on the incorporation of 14C-acetate and 14C-mevalonic acid into the non-polar lipids of the cells and the released lipids is being studied.